This is a follow-up to an earlier bugfix. It doesn't yet trigger any
known bugs but is a safety precaution since IfBuilder usage increases.

R=jkummerow@chromium.org
BUG=chromium:243868

Review URL: https://codereview.chromium.org/15832005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14882 ce2b1a6d-e550-0410-aec6-3dcde31c8c00